Patterned features in magnetic media are used for storing digital data that can be erased and rewritten. Patterned magnetic media is used in memory devices, such as magnetoresistive random-access memory (MRAM) and magnetic logic, and is being developed for use in storage devices, such as disk or tape drives. Patterned magnetic media on a disk or tape substrate can be referred to as bit-patterned magnetic media. In patterned magnetic media for storage devices, some of the patterned features are designed as storage elements of digital bits of data and other patterned features are designed for functions, such as providing servo information to position a read/write head.
Magnetic storage devices may store data in magnetic storage media by controlling the orientation of the magnetic field of a storage element. Writing techniques include generating a magnetic field through a storage element, which then induces a magnetic material (such as cobalt-based or iron-based particles, grains or domains) of the storage element to align with the induced magnetic field. When the induced magnetic field is removed, the alignment of the magnetic material of the storage element may remain. Reading techniques include various methods for measuring or sensing a magnetic orientation of the magnetic material of a storage element.
Generally, the magnetic material that is used to store data in disk drives and tape drives has adequately high magnetic moment density that can be reliably sensed by a read head. Highly magnetic materials have a large magnetic moment density, which promotes a strong and highly interactive magnetic field. Accordingly, magnetic materials with large magnetic moment densities generally make it easier to sense a magnetic orientation of the material because the field is easier to measure and/or sense.
Additionally, the magnetic material used to store data conventionally is a hard magnetic material. Hard magnetic materials tend to have a higher coercivity compared to softer magnetic materials. The higher coercivity of hard magnetic materials allows them to more stably maintain a magnetic orientation. Accordingly, using hard magnetic materials may allow a magnetic storage media to store data for long periods of time without refreshing or rewriting each bit of information. However, the high coercivity of a material may also make it more difficult to perform a write operation on the material. For example, in order to properly perform a write operation on a hard magnetic material, the magnetic field induced during a write operation may be required to have a higher magnitude or the induced magnetic field may be required to be applied for a longer period of time. Such additional requirements can lead to limitations on the areal density of magnetic elements formed in the medium because a higher magnitude magnetic field may affect nearby storage elements if the elements are too close to each other. Further, such additional requirements can also lead to slower write times because changing the magnetic orientation of a magnetic element with a magnetic field of a given amplitude may take longer.
Another challenge with patterned magnetic media is the reduced stability of the orientation of magnetic elements having smaller anisotropy and volume. Thermal affects alone, or in combination with static magnetic fields of neighboring storage elements, may induce smaller-sized magnetic elements that have low anisotropy to spontaneously change orientation. This results in the loss of stored information and loss of data. Because patterned magnetic media generally uses smaller and smaller portions of material for storing magnetic fields to increase storage density, the magnetic instability of a storage element becomes more and more of a limiting factor.
Several techniques are known for patterning bit-patterned magnetic media. Prior techniques relied on an etching process for forming the patterns of storage elements in data storage media. However, such techniques may require the planarization of the etched disk, which, if needed, result in increased cost and labor, as well as a reduction in yield. Accordingly, recently there has been a desire to develop certain techniques to mitigate the shortcomings of etching-based processes. For example, masked ion-beam and masked plasma immersion ion implantation lithography have proven to be an efficient alternative for producing patterned media.